The invention relates to hydromechanical power splitting transmissions for use between the prime mover and the axle power train of a vehicle, more particularly a commercial vehicle of the type comprising a planetary differential drive with at least two series of planetary wheels, two sun wheels, a web and an annulus, furthermore a drive input shaft and a drive output shaft, connected with different shafts of the planetary differential drive, with at least first and second hydrostatic machines, which in at least one operational range are connected with one shaft of the planetary differential drive and at least the first of said hydrostatic machines is able to be swtiched over from its own shaft to another on changing the operational range by means of clutches, while the second hydrostatic machine is at least substantially stationary.
Such s transmission has for instance been proposed in the U.S. Pat. No. 4,313,351, see FIG. 1. In such a transmission the output torque in reverse is only equal to approximately 50% of that during forward travel. This is due to the following reasons: during forward travel the torque of one hydrostatic machine connected to the output shaft and the torque of the prime mover and the supporting torque of the other hydrostatic machine (control power machine) are summated. In reverse on the other hand the torque of the prime mover and of the hydrostatic machine are subtracted from the torque of the hydrostatic machine connected to the output shaft. In reverse this leads to unsatisfactory drive conditions.